A varity of techniques have been employed in the past to detect (1) when a vending machine dispensing motor has returned to its home position after dispensing a product, and (2) when the product to be vended by that dispensing motor is soldout. Much of the art pertaining to vending machine product delivery motor home detection is described in U.S. Pat. No. 4,458,187 which is assigned to the assignee of the present invention and which is incorporated by reference herein. U.S. Pat. No. 4,458,187 describes a vending machine control and diagnostic apparatus for a vending apparatus having product delivery means such as an electrically operated actuator. An impedance element and a switch are connected in series with each other and in a parallel circuit with the actuator. Opening and closing of the switch are controlled by the operation of the actuator. Whether the actuator is in the appropriate position, open circuited or short circuited, is determined by the control and diagnostic apparatus' detection of changes in impedance of the parallel circuit. In several embodiments disclosed in U.S. Pat. No. 4,458,187, separate run and test signals are supplied to the actuator. In a further embodiment, a 24V DC run signal and a 5V RMS AC test signal are combined on a single wire. The test circuit in that embodiment includes a DC test circuit and an AC test circuit.
Additional prior art in the art of home detection is seen in control apparatus manufactured by Coin Acceptors, Inc. In particular, Coin Acceptors, Inc. employs a scheme which places a motor actuated single pole double throw switch in series with each motor. Home position is detected by detecting short switch opening occurring when the cam actuated switch very briefly opens and then closes at the home position. This scheme shorts the normal open and normal closed contacts of the switch. Only during switch transitions is a circuit "open" detected. This "open" is monitored and used to determine the home position. The system is fundamentally noise sensitive in that noise being received anywhere within the home detect circuitry may give a false home indication. Also, as the actual signal is non-repetitive, there is no way to "check again" the fact of the home position. Additionally, as motor current is passed through the switch contacts and is in fact switched by these contacts, switch life will be shortened.
A further product delivery motor home detection apparatus is described in Dobbins, "Vending Machine Control With Improved Product Delivery Motor Home Detection Motor Speed Control And Power Supply", U.S. Pat. No. 4,785,927 filed Mar. 2, 1987, and assigned to the assignee of the present invention. This application is also incorporated by reference herein.
With respect to detection of a soldout condition, the prior art as opposed to motor home detection, employed a number of different schemes to accommodate the soldout switches. Each of these schemes involves extra wiring which adds to the cost and complexity of the vending machine employing the scheme.
For example, in electronic controlled vending machine, the wiring to the motors is typically by a separate power lead to each motor and a common return lead to a row of motors. This is extended in the case of many motors to require a matrix of common row wires and common column wires. This is also the wiring scheme for the soldout switches, hence an additional set of row plus column wires is employed to sense a soldout condition.
Other less efficient schemes require up to 2 wires for each motor and 2 wires for the soldout switch.